Anti-vibration mechanism for vibrating body

Abstract: This invention relates to an anti-vibration mechanism supporting a vibrating body in a frame by a spring and a damper (9), and may be applied for example to a drum-type washing machine provided with a wash tank (3) that rotates about a horizontal axis. The damper has connections with the vibrating body (3) and frame (1), and a mechanism which creates a certain amount of clearance in one of these connections is provided. Further provided is a mechanism for supporting the damper on the frame such that it maintains the damper in any existing rotation position, but allows the damper to rotate when a rotating force higher than a predetermined level is applied to the damper. In the case of a washing machine, for example, the amount of clothes changes or the weight changes during washing or pumping of water. Accordingly the damper contracts or elongates as well as rotating to support the drum accommodating the wash tank. On the other hand, as there is always a predetermined amount of clearance in one of the connections, transmission of low amplitude vibrations via the damper is completely insulated while high amplitude vibrations beyond the clearance is effectively attenuated by the damper.

Description: FIELD OF THE INVENTION This invention relates to an anti-vibration mechanism which supports a vibrating body such as a wash drum in a washing machine so as to attenuate its vibration by means of springs and dampers. BACKGROUND OF THE INVENTION In drum-type washing machines provided with a tank which rotates about a horizontal axis, a drum is suspended by means of springs inside a wash frame, this drum housing a wash tank. The wash tank is rotated by means of a motor inside the wash frame via belts and pulleys. In this case, high frequency vibration due to high speed rotation of the tank is absorbed by the springs. However, if low frequency vibration occurs when water begins to be pumped out of the tank for example due to uneven distribution of clothes inside the tank, the wash frame may resonate as the rotation speed of the tank increases, and this generates a large noise. One method of attenuating this low frequency vibration consists of interposing a damper 90 between a drum 3 and a frame 1 as shown in Fig. 8. This damper 90 suppresses the low frequency vibration, and thereby prevents resonance of the drum 3. However, although this arrangement is effective for preventing resonance, high frequency vibrations on the contrary tend to be transmitted more easily to the frame 1 due to the damping effect of the damper 90. In order to solve this problem, Jikkai Hei 4- 36991 published by the Japanese Patent Office for example discloses a method which employs a damper with variable damping factor and a sensor which detects the resonance point. The damping factor is set at a high value until the drum speed passes the resonance point, and the damping factor is thereafter reduced so that the transmission rate of high frequency vibrations is decreased. However, as this anti-vibration device requires a damper of complicated structure, a sensor and a controller, it has a complex construction which makes it costly. In this arrangement, it is moreover difficult to completely eliminate the damping effect and frictional resistance due to elongation and contraction of the damper, and as the damper is operated at all vibration frequencies, it is not possible to completely shield the vibrating body from high frequency vibration. Further, as the damper is constantly operating, its lifetime and reliability are also affected by wear of moving parts and leaks from seals. Jikkai Hei 4-77881 published by the Japanese Patent Office discloses an arrangement wherein a rod of the damper and an eye connected to the drum or frame, are linked by means of a lock mechanism using a detent driven by a solenoid. However, as this device also requires a controller it is costly, and the robustness of the detent-type lock mechanism is questionable. Moreover, the lock mechanism occupies a considerable space due to the solenoid, and it is difficult to eliminate the friction between the rod and eye to zero when the lock is released. A further vibration-damping device for a washing-machine is known from DE-A-2 815 596. SUMMARY OF THE INVENTION It Is therefore an object of this invention to effectively reduce vibrations in all frequency ranges. It is a further object of the invention to provide an anti-vibration mechanism not affected by changes in the weight of the vibrating body. It is yet a further object of this invention to provide such an anti-vibration mechanism at low cost. In order to achieve the above objects, this invention provides an anti-vibration mechanism for a vibrating body enclosed in a frame comprising a spring and a damper. The damper has connections with the vibrating body and frame, The mechanism further comprises a mechanism for providing a clearance within predetermined limits in one of the connections, and a mechanism for supporting the damper on the frame. The supporting mechanism maintains the damper in any existing rotation position while allowing the damper to rotate when a rotating force higher then a predetermined level is applied to the damper. The supporting mechanism preferably comprises the connection between the damper and frame, this connection comprising a bush, bracket, bolt which passes through the bush and bracket, and a nut which generates friction between the bush and bracket when it is tightened on the bolt. The clearance providing mechanism preferably comprises an eye, a bolt and a shock-absorbing member which absorbs the shock between the eye and bolt The clearance is preferably set to be of the same order as or greater than the vibration amplitude in the high frequency vibration range of the vibrating body. This invention also provides an anti-vibration mechanism for a vibrating body enclosed in a frame comprising a spring and a rotary damper, this rotary damper having connections with the vibrating body and frame. Further provided is a mechanism for providing a clearance within predetermined limits in one of the connections. The clearance providing mechanism preferably comprises an eye, a bolt and a shock-absorbing member which absorbs the shock between the eye and bolt. The clearance is preferably set to be of the same order as or greater than the vibration amplitude in the high frequency vibration range of the vibrating body The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic front view of an interior of a drum type washing machine according to this invention. Fig. 2 is a schematic side view including a partial section of the interior of the drum type washing machine. Fig. 3 is a vertical sectional view of connections between a damper and a drum, and between the damper and a frame, according to this invention. Fig. 4 is a graph showing a relation between vibration transmission rate and wash tank rotation speed according to this invention. Fig. 5 is a vertical sectional view of a connection between the damper and the drum according to another embodiment of this invention. Fig. 6 is a schematic front view of an interior of a drum type washing machine according to yet another embodiment of this invention. Fig. 7 is a vertical sectional view of connections between a damper and a drum and between the damper and a frame according to the embodiment shown in Fig. 6. Fig. 8 is a schematic front view of an interior of a prior art washing machine. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Fig. 1 and 2 of the drawings, a drum 3 which is a vibrating body is suspended by four springs 8 inside a wash frame 1. A wash tank 2 driven by a motor 4 shown in Fig. 2 is housed inside the drum 3. The motor 4 is installed outside the drum 3, and a pulley 5 attached to the rotation axis of the motor 4 rotates a pulley 7 attached to the rotation axis of the wash tank 2 via a belt 6. The wash tank 2 is driven at different rotation speeds when washing is performed and when water is pumped out of the tank. Two brackets 11 project downwards from the drum 3, and two corresponding brackets 21 project upwards in the frame 1. Rods 10 of dampers 9 are attached to the brackets 11, the bases of the dampers 9 being connected to the brackets 21. An eye 15 shown in Figs. 1 and 3 is fixed to the end of each of the rods 10, and a bolt 12 which passes through this eye 15 is fixed to the bracket 11 by a nut 13. A collar 14, being a shock absorbing member, fits over the circumference of the bolt 12. The rod 10 and bracket 11 are free to undergo any relative displacement up and down or to the left and right of Fig. 1 within the annular space formed between the eye 15 and collar 14. The size of this annular space is set to be larger than the vibration amplitude of the drum 3 in the high frequency vibration region. This construction forms a connection between the damper 9 and the drum 3. Another eye 16 is formed at the base of the damper 9, and a bush 17 comprising an elastic material such as rubber is fixed to the inside of the eye 16. The bush 17 is gripped between washers 20, a bolt 18 passes through its center and a nut 19 screws onto the bolt 18 so as to fix the bush 17 to the bracket 21 with a predetermined force. Due to friction between the bush 17 and the washers 20, the bolt 18 and the eye 16 that are in contact with the bush 17, the damper 9 is kept at an upright position, while it can pivot about the bolt 18 when a load above a predetermined level is applied. If clothes are unevenly distributed inside the wash tank 2 of the drum-type washing machine, the tank 2 becomes an unbalanced rotating mass. This causes vibration to occur as the rotation speed of the wash tank 2 is increased from zero to pumping speed, thereby displacing the drum 3. The rate at which vibration is transmitted from the drum 3 to the frame 1 is a maximum when the rotation speed of the tank 2 reaches a resonance point situated between the washing speed region and pumping speed region as shown in Fig. 4, and the displacement or vibration amplitude of the drum 3 is also a maximum at this speed. If there is no damper 9 and the drum 3 is supported only by the spring 8, the drum 3 oscillates with a greater amplitude at the resonance point as shown by the dotted line in Fig. 4. On the other hand, if the drum 3 is supported only by the damper 9 as shown in the prior art shown in Fig. 8, although the vibration transmission rate at the resonance point is considerably less, the vibration of the drum 3 is then transmitted to the frame 1 via the damper 9 in the high frequency region, hence the transmission rate in the pumping speed region increases as shown by the solid line in Fig. 4. When the anti-vibration mechanism of this invention is used, the drum 3 tends to undergo a considerable displacement in the vicinity of the resonance point, and the bolt 12 of the bracket 11 comes into contact with the inner circumference of the eye 15 via the collar 14 so as to cause the rod 10 to elongate and contract. The damper 9 generates a damping force which opposes the elongation and contraction of the rod 10, hence the vibration energy of the drum 3 is absorbed by the damper 9 and the displacement of the drum 3 is suppressed. The impact and noise when the bolt 12 strikes the eye 15 are lessened by the collar 14 interposed between the bolt 12 and the eye 15. Impact and noise are suppressed also by the elastic bush 17 installed between the eye 16 of the damper 9 and the bolt 18. Therefore as shown in Fig. 4, at the resonance point and in its vicinity, effectively the same vibration attenuation is obtained as in the conventional case shown in Fig. 8 wherein the drum is directly supported by the damper. Although the drum 3 does undergo a displacement in regions other than that of the resonance point, for example in the washing region or pumping region shown in Fig. 4, this displacement is less than the gap between the inner circumference of the eye 15 and the outer circumference of the collar 14. The collar 14 therefore moves freely inside the eye 15 according to the displacement of the drum 3, and the rod 10 is not made to contract. In other words, as the drum 3 and damper 9 are effectively not in contact with each other, the vibration transmission rate of the drum 3 is effectively identical to the case wherein it is supported only by the spring 8, so the rate is very much less than in the case where it is directly supported by the damper as shown by the single dotted line. As the damper 9 is activated only at the resonance point and in its vicinity, the damper 9 does not transmit vibration in the high speed region as for example when water is being pumped out, hence the vibration transmission rate is very much suppressed both at the resonance point and during pumping. Moreover, as in the high frequency vibration region the damper 9 does not operate, the working time of the damper 9 is shorter than the operating time of the washing machine, and this also helps to maintain the lifetime and reliability of the damper 9. When the amount of clothes in the tank 2 varies, the amount of elongation of the spring 8 varies due to the change of supported weight, and the position of the drum 3 changes. For example, if the amount of clothes increases, the drum 3 moves downwards, and if this displacement exceeds the gap between the eye 15 and the collar 14, the eye 15 pushes the rod 10 down in contact with the collar 14. At the same time, the damper 9 turns against friction with the bush 17, and this restores the position of the damper 9 to a new pivot angle at which a balance is obtained. Therefore, even if the support position of the drum 3 changes, the clearance between the eye 15 and the collar 14 does not change, and good vibration suppression is still maintained. Fig. 5 shows another embodiment of this invention wherein the connection between the rod 10 and the bracket 11 differs. Here, a cushion 30 is installed on the inner circumference of the eye 15 instead of the collar 14 which fits over the outer circumference of the bolt 12. This cushion 30 has the same shock absorbing effect as that of the collar 14 when the eye 15 strikes the bolt 12. In the aforementioned embodiments, the damper 9 was supported on the base of the frame 1, however it may also be supported at the side of the frame 1, and the number of dampers may moreover be varied as required. Further, the eye 15 may also be installed on the bracket 11, and the bolt 12 installed on the rod 10. A rod or a tube may also be used instead of the bolt 12. Figs. 6 and 7 show yet another embodiment of this invention, in which a rotary damper 40 is used instead of the linear type damper 9. The rotary damper 40 comprises an arm 41, and a rod 10 is hinged at the tip of the arm 41. As shown in Fig. 7, the connection between the rod 10 and bracket 11 has the same construction as in the first embodiment. The connection between the rotary damper 40 and bracket 21 has the same construction as the connection between the damper 9 and bracket 21 of the first embodiment. However, since the arm 41 is rotatable, it is also possible to fix the damper 40 to the frame 1. In the aforementioned embodiments, a clearance was provided between the bracket 11 and the rod 10, however, a clearance may also be provided between the damper 9 or 40 and the bracket 21. Moreover, in the washing machine shown in Fig. 6, such a clearance may also be provided in the connection between the arm 41 and the rod 10. Finally, each embodiment of the invention has been described in the context of its application to a drum type washing machine, however the invention is not limited to a washing machine and may in general be applied as an anti-vibration mechanism to any vibrating body. The embodiments of this invention in which an exclusive property or privilege is claimed are defined as follows:

Claims: An anti-vibration mechanism for a vibrating body (3) enclosed in a frame (1), comprising a spring (8) and a damper (9), said damper (9) having connections with said vibrating body (3) and frame (1), each of said connections being constructed around an axis, at least one of said connections comprising means for supporting said damper (9), said supporting means maintaining said damper (9) in any existing rotation position while allowing said damper (9) to rotate when a rotating force higher then a predetermined level is applied to said damper (9), characterized in that at least another one of said connections is arranged such that between said axis and said connection there is provided an annular space to allow considerable movements of the connection with respect to the axis for a predetermined range of vibration amplitudes without contacting said axis. An anti-vibration mechanism as defined in claim 1, characterized in that said supporting means comprises the connection between said damper (9) and frame (1), said connection comprising a bush (17), bracket (21), bolt (18) which passes through said bush (17) and bracket (21) and a nut (19) which generates friction between said bush (17) and said bracket (21) when it is tightened on said bolt (18). An anti-vibration mechanism as defined in claim 1 or 2, characterized in that said annular space is defined by an eye (15), a bolt (12) and a shock-absorbing member (14) which absorbs the shock between said eye (15) and said bolt (12). An anti-vibration mechanism as defined in at least one of the proceeding claims 1 to 3, characterized in that the thickness of the annular space in radial direction is set to be of the same order as or greater than the vibration amplitude in the high frequency vibration range of the vibrating body (3). An anti-vibration mechanism as defined in at least one of the preceding claims 1 to 4, characterized in that said damper is a rotary damper (40), having connections with said vibrating body (3) and frame (1). An anti-vibration mechanism as defined in claim 5, characterized in that said annular space is defined by an eye (15), a bolt (12) and a shock-absorbing member (14) which absorbs the shock between said eye (15) and said bolt (12). An anti-vibration mechanism as defined in claim 5, characterized in that the thickness of the annular space in radial direction is set to be of the same order as or greater than the vibration amplitude in the high frequency vibration range of the vibrating body (3).

Inventors: KASHIMA MITSUHIRO, MATSUMOTO HIROSHI, KASHIMA, MITSUHIRO, MATSUMOTO, HIROSHI, KASHIMA, MITSUHIRO, C/O KABAYA KOGYO K.K., MATSUMOTO, HIROSHI, C/O KABAYA KOGYO K.K.
Applicants: KAYABA INDUSTRY CO LTD, KAYABA KOGYO KABUSHIKI KAISHA
Application year: 1994
Main classification: D06F37
IPC codes: F16F9, D06F37, D06F49